Many beverages, such as beer and soda, are often stored in a container, or keg. In the case of carbonated beverages, the keg is capable of withstanding elevated internal pressures to retain a level of dissolved carbon dioxide in the beverage during storage as well as providing a means to drive the beverage out of the keg while serving. The beverage in a keg is generally served by applying pressure, from an external source, to the contents of the keg, thereby pressurizing the keg and forcing the beverage out through a spout. The pressure is often supplied in the form of compressed gas injected into the keg. The compressed gas can be supplied manually from a hand-operated pump, in which case the gas is generally comprised of ambient air. Or, the compressed gas can be supplied by a pressurized tank containing an inert gas, such as carbon dioxide or nitrogen.
In the case of carbonated beverages, which contain dissolved carbon dioxide, carbon dioxide gas is frequently used to pressurize the keg for the purpose of serving the beverage. In addition, the introduced carbon dioxide maintains the dissolved level of carbon dioxide in the beverage, thereby preventing the beverage from going “flat.”
Over-pressurizing the keg can lead to a number of undesirable results. First, a keg may burst when exposed to an internal pressure exceeding design limits. This can result is spillage of the contained beverage and potential injury to nearly persons and/or property. Secondly, over-pressurization will over-carbonate the beverage, potentially altering the character and taste of the beverage. Finally, over pressurization can result is excessive foaming of the dispensed beverage.
Some common pressurization methods, such as a hand-driven pump, cause the pressure in the keg to cycle above and below the optimum pressure necessary to serve the beverage and to maintain the proper level of dissolved carbon dioxide in the beverage.
Pressurization methods that use a single stage pressure regulator combined with a high pressure gas source either cannot (a) provide the relatively low pressure necessary to maintain the proper level of dissolved carbon dioxide in the beverage or (b) controllably maintain such a level with sufficient accuracy. For example, compressed gas sources generally provide pressure at about 850 psi in the case of carbon dioxide. The pressure to maintain the proper level of dissolved carbon dioxide for some beverages is 12 psi. The pressure of the gas source is thus roughly 70 times the desired serving pressure. Single stage pressure regulators either cannot achieve the 70 times reduction in pressure or cannot achieve the desired serving pressure with any accuracy or consistency.